Dynamic Structures

Adaptive Optics

Many large telescopes now employ adaptive optics on either their primary or secondary elements to counter the effects of constantly changing atmospheric conditions. The actuators for the adaptive system are typically piezo elements attached to the back of flexible elements. Measuring adaptive optics to understand how they respond to changes in their controlling actuators is critical to excellent performance.

In the past, to measure the modal response of adaptive optics to changes in the actuators, sensors have been used to measure movement at individual points on an optic—a slow, low-resolution solution.

4D dynamic laser interferometers measure nearly instantaneously, so they can image adaptive optics as they are actuated, and verify and calibrate the response of the actuators. Dynamic interferometers show the 3D response of the entire optic, providing a complete image of control system performance.

4Sight analysis software, included with all 4D interferometers, offers a modal analysis option which allows engineers to view the mirror response in real-time and to adjust the adaptive optic system accordingly.

Diffuse Surfaces

The SpeckleCam Electronic Speckle Pattern Interferometer (ESPI) measures the change in shape of structures with diffuse surfaces up to several meters in diameter. Rapid data acquisition permits accurate testing and quality control on the production floor, without the need for costly vibration isolation hardware.

With the ESPI, a baseline measurement is made, then subsequent measurements are compared to it, to determine deformation. Measurements can be made synchronously or asynchronously with respect to object motion. For measurement of vibrational deformation, synchronous capture can examine changes over a wide frequency and phase spectrum.

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